pola-rs/polars · error · ValueError

cannot {operation}: no data_source_format found

Error message

cannot {operation}: no data_source_format found

What it means

Companion to the missing-location error: `_extract_location_and_data_format` (client.py:746) requires both `storage_location` and `data_source_format` on the Unity Catalog TableInfo. Polars dispatches on the format (DELTA/DELTASHARING get Delta-specific reads/writes, PARQUET/CSV/etc. get plain cloud reads), so a null `data_source_format` raises ValueError 'cannot scan table: no data_source_format found'. It means the catalog returned table metadata that does not declare what physical format the files are in.

Source

Thrown at py-polars/src/polars/catalog/unity/client.py:755

            msg = (
                "did not receive credentials from temporary credentials API for "
                f"{table_id = }"
            )
            raise Exception(msg)  # noqa: TRY002

        yield creds, expiry


def _extract_location_and_data_format(
    table_info: TableInfo, operation: str
) -> tuple[str, DataSourceFormat]:
    if table_info.storage_location is None:
        msg = f"cannot {operation}: no storage_location found"
        raise ValueError(msg)

    if table_info.data_source_format is None:
        msg = f"cannot {operation}: no data_source_format found"
        raise ValueError(msg)

    return table_info.storage_location, table_info.data_source_format

View on GitHub (pinned to df599052da)

Solutions

1. Inspect `client.get_table_info(...).data_source_format` first and fail with a clear message if None
2. Recreate/repair the table registration so it declares a format (e.g. CREATE EXTERNAL TABLE ... STORED AS PARQUET LOCATION ..., or resync via UC)
3. If the underlying files are Parquet/Delta and you know the path, read them directly: `pl.scan_delta(location)` or `pl.scan_parquet(location)` with the storage_location and credentials you already have
4. Upgrade the polars-cloud/unity SDK client if a stale API version is dropping the field

Example fix

# before
lf = catalog.scan_table("main", "sales", "legacy_synced_tbl")  # data_source_format is None

# after
info = catalog.get_table_info("main", "sales", "legacy_synced_tbl")
if info.data_source_format is None:
    # bypass catalog dispatch, read the files directly
    lf = pl.scan_parquet(info.storage_location, storage_options=...)  # requires location
else:
    lf = catalog.scan_table("main", "sales", "legacy_synced_tbl")

info = catalog.get_table_info(catalog_name, namespace, table_name)
if info.data_source_format is None:
    raise ValueError(f"table {tbl} declares no data_source_format; cannot dispatch reader")

from polars.catalog.unity.models import TableInfo

def has_known_format(info: TableInfo) -> bool:
    return info.data_source_format is not None

try:
    lf = catalog.scan_table(cat, ns, tbl)
except ValueError as e:
    if "no data_source_format found" in str(e):
        # fallback: read the raw files if location exists
        info = catalog.get_table_info(cat, ns, tbl)
        if info.storage_location and info.storage_location.endswith(('.parquet', '/')):
            return pl.scan_parquet(info.storage_location, storage_options=storage_options)
    raise

When it happens

Trigger: `catalog.scan_table(...)` or `catalog.write_table(...)` on a table whose UC metadata has data_source_format = null: typically non-Delta external tables registered without a format, foreign tables, objects created by third-party metastore sync tools, or an older UC workspace/API version that does not populate the field for the object type being read.

Common situations: Hive metastore-to-UC migrations that leave format null on synced tables; tables created via direct REST 'createTable' calls that skipped data_source_format; reading views or system objects never intended to be scanned; SDK version older than the workspace API returning sparse metadata.

Related errors

• cannot {operation}: no storage_location found
• a non-HTTPS workspace_url was given ({workspace_url}). To al
• cannot apply delta_table_version for table of type {data_sou
• cannot apply delta_table_options for table of type {data_sou
• write_table: table format of {catalog_name}.{namespace}.{tab

AI-assisted analysis of pola-rs/polars@df599052da (2026-08-16). Data as JSON: /api/errors/d9d70e3501806c23. Report an issue: GitHub.